Similar electric machines are designed in particular as asynchronous machines, but also as permanent or externally excited synchronous machines, and they have been considered already for some time for the drive of motor vehicles. A sheet metal package is provided for the construction of the stator, which has slot-like receptacles for the stator windings that are mutually insulated from one another. The receptacles can be closed by a closure element, which is often referred to as a slot wedge. The stator windings are typically fed via an inverter, which converts multi-phase alternating voltage in the kilohertz range from a direct voltage. For a switching element of the inverter are usually employed power semiconductor components such as IGBT or GTO.
Moreover, a capacitive coupling of these components is created with the electrically insulated arrangement of the stator windings opposite the rotor on the one hand, and of the capacitive coupling of these components of the sheet metal package on the other hand. In addition, the switched on inverters have also a voltage zero component, which provides a common mode voltage for the reference potential, in particular for the ground potential. Through so called parasitic capacities, the common mode voltage is applied to a shaft of the electric machine and it generates in this manner a shaft voltage for the reference potential. At the same time, so-called du/dt currents occur in particular at one or at several bearings of the machine. In addition, the shaft voltage generates stochastic breakdowns with the bearing lubricant, which leads to an erosion of sparks (electrical discharge machining, EDM) of metallic bearing components. These EDM currents can lead to bearing damage within a relative short operating time period.